Having already lost one key member of the front office who probably did not get as much public credit as he deserved, the Celtics managed to avoid losing a second member of their successful front office this offseason. Mike Zarren, who has been believed to be a serious candidate for the general manager’s job in Philadelphia since last summer, reportedly turned down that job this offseason. Two league sources told Steve Bulpett of the Boston Herald that Zarren declined an offer from the Sixers. Philadelphia eventually hired Sam Hinkie, formerly the executive vice president of basketball operations in Houston. Zarren declined comment to the Herald, but this is not the first (or last) job the Celtics assistant G.M. and team counsel has been linked to. Zarren began his career in the NBA as an unpaid intern with the Celtics, and he is described in the team’s media guide as being a lifelong Celtics fan. Ryan McDonough, the team’s other assistant G.M., was named last week as general manager of the Phoenix Suns.